Opponents of Hugo Chávez unleashed a fresh burst of accusations against the Venezuelan president Friday, a day after a former close collaborator of Mr. Chávez turned ardent foe was arrested at gunpoint on corruption charges.

One Chávez rival, Antonio Ledezma, the mayor of metropolitan Caracas, denounced the president as a tyrant who's trampling on the Venezuelan Constitution by stripping officials such as he of power and punishing political enemies with jail.

"Dictatorship, no! Democracy, yes!" they shouted. "Let's take it to the streets!"

The rally occurred as Raúl Isaias Baduel, who broke with Chávez in 2007 after resigning as defense minister, was arraigned at a military court in Caracas on charges of stealing $19 million in public funds. A military judge ordered that Mr. Baduel be kept behind bars to prevent him from fleeing the country.

A Caracas radio station quoted Baduel as declaring his innocence and saying that an unmarked car had intercepted his wife and him at noon Thursday in Maracay, 60 miles west of Caracas.

"A group of individuals pointed their weapons at my wife and me and demanded that we accompany them," Baduel said, adding that he was the victim of "a cowardly act ordered by Hugo Chávez."

Ismael Garcia, who heads an opposition political party, told the noontime rally Friday that the president's opponents would defend Baduel.

"I want to call out the generals and admirals in charge," Mr. Garcia said. "You will be responsible for this tragedy in our country."

Chávez appears to be tightening his grip on power at a time when analysts are predicting that Venezuela is entering a recession that will force the president to cut spending for the poor. Oil income, which accounts for half the government's revenue, is expected to drop by 50 percent this year.

Pollsters are predicting that Chávez's popularity will decline, limiting his ability to maneuver.

Besides Baduel, another high-profile Chávez opponent, Manuel Rosales, is facing an arrest order for alleged corruption. Mr. Rosales, who lost the 2006 presidential election to Chávez, was reported to be hiding in the city of Maracaibo, where he serves as mayor.

Rosales' supporters say that Chávez wants him silenced, pointing to an incendiary comment by the president last year before a roaring group of supporters.

"I'm going to put you in jail, Rosales!" Chávez proclaimed.

At Friday's rally, Ledezma said that Chávez was violating the will of voters by having his allies in Congress approve a measure turning over many of Ledezma's powers to a government-appointed official.

Ledezma, who took office late last year, has been hamstrung by having armed government supporters occupy the mayor's offices, forcing him to work out of a makeshift office elsewhere.

While the opposition was attacking the president in Venezuela, Chávez was meeting with Iranian President Mahmoud Ahmadinejad in Tehran. There, he mocked the G-20's efforts to refloat the global economy through more bank loans, investment and trade.

"It's impossible that capitalism can regulate the monster that is the world financial system. It's impossible," Chávez told a Venezuelan state television channel. "Capitalism needs to go down. It has to end. And we must take a transitional road to a new model that we call socialism."

A climate of fear, which has waxed and waned during Chávez's 10 years in office, seems to be on the rise in Venezuela.

"Some journalists have asked me if I'm afraid," Ledezma said at the rally. "Of course I'm afraid. I'm a human being. But I'll keep fighting. Better to fight than live on your knees!"

When the event ended, Ledezma strode away, surrounded by a phalanx of bodyguards.